I am currently reading the Full text of "the story of old Halifax" which reads following:

January 23rd, 1643, he marched "against Leeds, and after a desperate fight, re-captured the town. The war-cry of Fairfax's army was "Emmanuel."

Major Forbes was the first man to enter, by climbing over the wall, by standing on the shoulders of Lieutenant Horsfall of Halifax. When they had entered the town, Mr. Jonathan Scholefield, minister of Cross-Stone Chapel, (near Todmorden) started the singing of a psalm: —

" Let God arise, and scattered Let all His enemies be ; And let all those that do Him hate, Before His presence flee,"

According to the account of the fight, several Halifax men had marvellous escapes. Fairfax praised his soldiers. He called them unexperienced fresh- water men, yet although they had only received a week's training, they attacked most resolutely and valiantly. The Earl of Newcastle retreated to York, but before long he was vigorously pressing the Fairfaxes with a larger army.

So looks like Leeds did have a surrounding wall, at first I thought would have probably been defensive ditches thrown up by the soldiers occupying the town but saying that he entered by standing on the shoulders of another man they must've been quite substantial, the walls at York in some parts could've been climbed by standing on the shoulders of someone else the walls down marygate for example are not that high really.